Low-conductivity mold for centrifugal casting machines



d 'July 3\1,1'92a 1,678,929Y

` L. YEoMANs IQOVI CONDUCTIVITY MOLD FOR CENTRIFUGAL CASTING IIACHINS Filled July 17, 1924 IN VENTOR. W/m/Esss" Zua'ewZ'Yeama/m ATTORNEYS.

Patented July 31, 1928.

PATENT OFFICE.

LUCIEN I. YEOMAN S, OF CHICAGO, ILLINOIS, ASSIGNOR TO OF MILWAUKEE, WISCONSIN, A CORPORATION A.- o. 'SMITH CORPORATION,

oF NEW .Yoan v ITOW-CONDUCTIVITY MOLD FOR CENTRIFUGAL CASTING MACHINES.

Application ledJuly 17,

The invention relates primarily to the rotating molds of centrifugal casting machines, the purpose of the invention being to provide an improved special construction of\metal I mold whichv possesses the very desirable .property of comparatively low conductivity, and by means of which it is quite possible to control to an advantageous degree the rapidity with. which the heat-is transferred to the mold by abstraction from the molten metal when the latter is mold.

In ordinary molds of this class, the rate of heat transference from the molten metal poured into the forming the casting to the mold isvery unduly while the molten metal which has been poured thereinto is congealing, for the reason that the mold structure is liable to damage when such conditions arise. If an excessive temperature be permitted to persist in the mold during successive casting operations, the mold will become unserviceable within a. brief period of time.

My invention resides in an improved mold which is comprised of a plurality of concen-y trically arranged metal tubes or cylinders,` the contacting surfaces of which are in close engagement, so as to constitute a unitary structure, and yet the structure is one in which contacting surfaces of the tubes act as barriers to the quick passage of the heat from one to the other` so that permeation of the laminated structure by the heat is rendered slow in such a degree that abundant time is allowed fo-r withdrawing the cast-ing from the mold, with a consequent limitation upon the creation of conditions by which the mold might be adversely affected.

An advantage residing in my invention lies in its embodiment in a constructionl which will permit the innermost tube of the mold to be replaced, as occasion therefor may arise, without any material impairment of the value of the mold as a whole. When i924. serial no. 726,446.

in use, as is well known,

the inner surf of the mo'ld is subjected to me the greatest temperature variations, by reason of its directA contact with the molten metal, and the condition oistate of lpreservation of such inner surface determines thev period of serviceability of the mold. of the mold should become defective in such a degree as toreflect its condition upon the castings, or otherwise, the damage may be easily remedied by simply replacing the affected part by'another.

The details of my invention will now be described, and the novelty thereof pointed out in the appended claims.

In the drawings herewith: `Figure 1 is a longitudinal verticalA sectional v view of a centrifugal casting machine assembled with one of my improved molds as an element thereof.

Fig. 2 is an end view thereof, looking from the right of Fig. 1, this view being partly broken out'to show the construction of the mold.

Fig. 3 is a diagrammatic representation illustrating the time factors of the heat transference involved in the use of my improved mold. Referring tothe drawing, the numeral'lO indicates a tubular, balanced mold, supported at each end for rapid rotation upon the .sets of rollers 11, 11', journalled in stands If the inner surface or boxes 12, 12, the rollers of each set being spaced apart in parallelism with the axis of the mold, so as to revolubly support the latter. at its lower side. The mold is held 1n frictional engagement. with the rollers l1, 11', upon which it rests, by means lof other rollers 13,18', carried in caps or frames 14, 14, hinged at 15 lto the stands or boxes 12, 12, and provided with tension means 16, attached to the stands or boxes and bearing upon the caps or frames, for exerting pressure upon the rollers 13, 13. By disengag-l ing the tension means, the caps or frames 4may be turned on their pivots, and the mold removed. A fixed annular band 16 encircles the mold l0, and determines the longitudinal position of the mold in the casting machine, the said band 16 being received in and filling the space between two rollers 17, 17 which engage by their peripheries the said band at its opposite sides. The rollers 17, 17, are conveniently journalled in a stand 18 at the under side of the mold, the axes of the said rollers being vertically disposed in the said stand.

By means of a driving pulley 20 attached at one end to the mold 10, a rapld and C Ontinuous movement of rotatlon may belm- Aparted to the latter. The mold 1s p rovlded with end pieces or gates 21, 21', having circular flanges 22, 22 which are entered 1n the ends of the mold and act as dams to limit the outward longitudinal flow of the metal and define the length of the casting formed in the mold. The end pieces or gates 21, 21', one or both, are provided with a central opening through which the molten metal which is to form the casting may be mtroduced into the mold. 'lhe end pieces or gates are removably connected to the mold, so that one or both may be taken olf to enable the casting to be withdrawn from the mold. A convenient method of mounting the end pieces or gates, whereby theymay be quickly removedand replaced, 1s illustrated in theprovision of studs in the ends of the mold, such studs being transversely perforated on radial lines for the recept1on of keys, which latter are driven outwardly and there-fore not liable to displacement 1n the rotation of the mold.

Myy improvement resides in -the specific construction of the mold 10, which as hereinbefore indicated is constituted as an assembly of a. lurality of concentrically arranged .metal tu es or cylinders of different diameters. I have shown three of such cylinders, indicated by the numerals 23, 24 and 25. The assembly of the tubular elements of the mold may be effected in any suitable manner, such as force-fits, shrink-fits, or other means usual in connecting such bodies, so as to bring their contiguous surfaces into goed mechanical contact. It will be expedient to have the tubes of the same length, but this arrangement may be varied somewhat.

In constructing the improved mold so as to endow it with the very desirable feature of low conductivity, I make use of well known natural laws governing the transmission of heat through metallic surfaces. The time in which such transfer is effected is the sum of five factors, which are: (1) The nature of the surface film at the entrance surface of the plate, and its capacity for ready heat transmission, (2) the nature of the surface resistance of the plate in the entrance surface, which varies with variations in the nature and section of the surface, (3) the internal conductivity of the metal ofthe plate, which varies little in the same metal and directly in the temperature difference, (4) the natureof the surface resistance of the plate in the side opposite the entrance, and (5) the nature of the surface film of the plate at the side opposite the entrance, and its capacity for ready heat transmis- S1011.

The internal conductivity of the metal I itself (3), regardless of thickness is very small com ared to the resistance to conductivity of t e surface films (l and 5) and the surface boundaries (2 and 4.). As -anillustration of this fact, a layer of carbon dioxide only 1-6000th part of an inch, or 1-12th as thick as a line human hair, or a layer of Water 1-5000th of an inch thick, offers the same resistance to the percentage of heat that is presented by solid iron one inch in thickness. Heat transferred through a solid from a high to a low temperature joins by simple molecular commutation, and this is the internal conductivity by which alone heat could not flow beyond the boundary limits of one piece of substance. When it reaches the boundary of' a substance, it may be communicated to another contiguous substance, but at a retarded rate-of transfer. Rapid transfer ends with the limit of molecular cohesion, and beyond the boundaries of a substance, encounters a resistance through joints or between plates at the point of contact, no matter how perfect the mechanical juncture or adhesion may be There is then, in addition to the resistance of the surface films of contiguous parts, a real joint or surface resistance of unknown eX- tcnt and character at the boundary of every substantial body. The presence ofthisproperty is well known, and some boiler inspection laws forbid the locationV of seams where they will be brought into contact with fire, because experience has shown that the plates in the region of such seams frequently burn away. This burning is due to the nature of the joint resistance.

The thickness of the several tubes or cylinders of which the composite or laminated mold is constituted may be varied in accordance with the nature of the article which it is desired to produce, and thereby a wide relation of the time and the transmission of the heat may be determined and controlled. v

Fig. 3 of the drawing illustrates diagrammatically the manner in which the transference of heat from one to another of the several laminations used in my improved construction of mold is retarded and controlled. I have shown three of such laminations, indicated 23, 24 and 25, these numerals having been used hereinbefore to designate the laminations in Fig. 1, and have indicated by the vertical column vof numerals appearing in connection with the said Fig. 3, arbitrary periods of time, representing comparatively fractional seconds, which are required for the heat to penetrate and traverse one of the sections. Starting at zero, it will require approximately 5 periods of time for the heat to penetrate the surface film of the first plate 23. But such penetration having been effected, the hat instantly traverses the plate, and is arrested by the film surface at the opposite side. A like period of time as at the beginning is required for the penetration of this surface.

The heat must then pass through the contiguous surface of the adjoining or second plate 24, for the penetration of which a period of time equal to that in the first instance will be required. Upon penetration of the surface, the heat instantly traverses the second plate 24, but is again arrested by the surface film at the opposite side. Again the percentage of heat is retarded as before, but when penetration is eecte'd,`the percentage of the heat is further retarded by encountering the contiguous surface of the third plate 25, which will offer a like resistance for an equal period of time. But such penetration having been effected in the third late, the latter is immediately traversed by the heat, which then must penetrate the opposite and outer surface of the third plate.

My improved construction enables me to so control the transference of the heat from the molten metal to the mold, that the freezing of the molten metal is retarded to such a degree that before solidiication occurs in the molten metal, all of the gases and extraneous substances will have been expelled from the casting by the centrifugal action exerted upon the heavier mass of the molten metal. The invention may be used in connection with any of the usual coolingl devices known in the art, and is particu arly ellicient when cooled by the introduction of Water in the manner disclosed in my application Serial No. 7 26,445, filed herewith and on which Letters Patent No. 1,630,045 were granted May 24, 1927.

Having thus described my invention, what I claim and desire to secure by Letters Patent of the United States, is;

1. A rotatable, balanced mold for metal casting comprising a plurality of circular tubes of different diameters and concentrically assembled one Within another to form a unitary structure, and held together by the frictional engagement of the outer surface of one tube with the inner surface of the next larger tube.

2. A rotatable, balanced mold for metal casting comprising an assembly in one structure of a plurality of concentrically arranged circular tubes of different diameters, the exterior surface of one tube being in close engagement with the interior surface of an adjacent tube, and held together by the frictional engagement of the outer surr face of one tube with the inner surface of the next larger tube.

3. A rotatable, balanced mold for metal casting comprising a plurality of circular tubes of different diameters but of equal or substantially equal lengths and concentrically assembled one within another to constitute a unitary structure, and held together by the frictional vengagement of the outer surface of. one tube with the inner surface of the next larger tube.

4. A rotatable, balanced laminated mold comprising a plurality of concentrically arranged circular tubes of different diameters but of equai length, and in which a larger tube closely embraces the next smaller tube to present adjacent surfaces constituting barriers to retard the passage of the heat of the casting metal from one tube to the other` and held together by the frictional engagement ofthe outer surface of one tube wlth the inner surface of the next larger tube.

In testimony whereof, I have signed my name at Milwaukee, this 15th day of July, 1924.

LUCIEN I. YEOMANS. 

